This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The specific aim is to compare quantitative parameters of thymopoiesis from adolescents/young adults with perinatal HIV infection (PI-A) with those from age-matched seronegative control subjects (SN-A), and youth with HIV infection acquired via recent adult behaviors (AB-A).